In choosing Rep. Paul Ryan of Wisconsin as his running mate Saturday, Republican presidential candidate Mitt Romney tapped someone who has the power to energize the Republican Party’s base – and the Democratic Party’s, too.

The presence on the GOP ticket of Ryan, the House of Representatives Budget Committee chairman, whose plan to cut taxes, reduce spending and revamp Medicare is regarded as a Republican Party road map, ensures that two very different visions of the role of the federal government in America will be front and center in this fall’s presidential campaign.

Ryan, 42, wasted no time Saturday in framing the Republican case against President Barack Obama.

“I hear some people say that this is ‘the new normal,’ ” Ryan said in Norfolk, Va., with the battleship USS Wisconsin as a backdrop. “High unemployment, declining incomes and crushing debt is not a new normal. It’s the result of misguided policies.”

He and Romney then began a tour that took them through Virginia on Saturday and had them scheduled to visit North Carolina, Florida and Ohio next, all states Obama carried in 2008 and that Romney must win if he is to unseat the president.

The new Republican ticket was well received in Virginia. Charlie DeGraw, 63, the owner of Charlie D’s Next Day Tees, drove to a Romney-Ryan rally in Manassas, Va., after watching the Norfolk event on Fox News. He stopped by his shop and printed out a neon green Romney-Ryan 2012 T-shirt for the occasion.

Barry Gill, 29, who attended the Manassas event with his wife and three children, said the Ryan pick surprised him. He preferred Rubio as a running mate and thinks Ryan could be more effective remaining in the House.

“I’m a big fan of Ryan’s budget,’ he said. “It’s a double-edged sword.”

The Obama team welcomed Ryan, a seven-term congressman, to the campaign trail with a blistering critique.

“In naming Congressman Paul Ryan, Mitt Romney has chosen a leader of the House Republicans who shares his commitment to the flawed theory that new budget-busting tax cuts for the wealthy, while placing greater burdens on the middle class and seniors, will somehow deliver a stronger economy,” Obama campaign manager Jim Messina said.

Romney’s announcement ended a four-month search that was shrouded in speculation, secrecy and questions about whether he’d play it safe and select a steady but unspectacular running mate, such as Sen. Rob Portman, R-Ohio, or former Minnesota Gov. Tim Pawlenty, or make a bold statement by choosing someone such as Florida’s Sen. Marco Rubio, who’s Hispanic, or a woman such as Sen. Kelly Ayotte, R-N.H.

Romney seemed so excited about his choice Saturday that he inadvertently introduced Ryan as the next president of the United States.

“Every now and then I’m known to make a mistake,” Romney said, interrupting the start of Ryan’s acceptance speech. “I did not make a mistake with this guy.”

In the end, Romney managed to pick someone who was both a safe and bold choice, several political experts said.

“It’s safe in that Paul Ryan fits Mitt Romney’s comfort zone. He’s an extension of the (Romney) family; he’s as young as one of Romney’s sons,” said Tim Walch, the editor of a book of essays on the vice presidency, “At the President’s Side: The Vice Presidency in the Twentieth Century.” “And he’s the type of person Romney worked with at Bain Capital: whip-smart, kind of a wonk who can break down policy to find solutions. It’s bold because it really energizes the right wing of the Republican Party at the time Romney needs a boost the most.”

Romney appears to have heard the chorus of party conservatives and deficit hawks who were clamoring for Ryan on the ticket. Before Saturday’s announcement, many of those voices had worried about Romney’s political compass and feared that he might become more moderate in the general election.

“Paul Ryan is a solid conservative leader whose conservatism is indivisible,” said Ken Blackwell, a former Ohio secretary of state who’s a board member for the fiscally conservative Club for Growth and the National Taxpayers Union. “His commitment to advancing American exceptionalism is rooted in his embrace of our pro-life, pro-family, pro-growth, pro-defense traditions.”

But Ryan’s rise to the vice-presidential nomination carries risks. He galvanizes Republicans, but he also energizes Democrats, who despise his budget plan. Democrats said they looked forward to using him as a foil to show what’s wrong with Romney’s and the Republican Party’s policies and rhetoric.

Several Democrats eagerly noted Saturday that Ryan likes to talk tough about deficits and the evils of government entitlement programs yet he voted for the Medicare Part D prescription-drug expansion in 2003 and the Troubled Asset Relief Program in 2008, which bailed out some of America’s biggest financial institutions.

“Now with Congressman Ryan on the ticket, House Republicans face the one thing they hoped to avoid: a national debate on their budget that puts millionaires first and Medicare and the middle class last,” said Rep. Steve Israel of New York, the chairman of the Democratic Congressional Campaign Committee.

The general public hasn’t embraced Ryan’s plan to overhaul Medicare, though it’s popular among many conservatives. A CNN/Opinion Research Corp. poll in June 2011 found that 58 percent of Americans opposed the Republican Medicare plan while 35 percent said they supported the measure. Among senior citizens, who compose a sizable voting bloc in swing states such as Florida, 74 percent opposed the Republican-proposed Medicare plan.

Another potential problem the Romney-Ryan ticket faces is a lack of foreign-policy expertise. Recent successful presidential candidates with few foreign-policy credentials have balanced their tickets with running mates known for their expertise in international affairs, intelligence or defense expertise: Dick Cheney for President George W. Bush; Al Gore for President Bill Clinton and George H.W. Bush for President Ronald Reagan.

“They’ve obviously made the determination that the election is about the economy,” Walch said.

Romney is betting that he and Ryan can buck history and have a member of the House become vice president. That happened only three times in the 20th century, Walch said: James Sherman, a House member from New York, was William Howard Taft’s vice president; John Nance Garner, a Texan and House speaker, was elected Franklin D. Roosevelt’s vice president; and Gerald Ford was appointed vice president after Spiro Agnew resigned as Richard Nixon’s number two after pleading no contest to tax evasion.

“Serving as a congressman generally does not give you a boost on the national ticket,” Walch said. “Recent vice-presidential nominees who came directly from the House, such as Geraldine Ferraro, are rare indeed.”

But times have changed. The profile of the 435-member House – considered the junior circuit to the 100-member Senate – has risen in recent years thanks, in part, to the dramatic shift in power from Democratic to Republican control in 2010 and the influx of tea party members, and Ryan has been one of its most high-profile lawmakers.

Ryan’s budget plan is widely regarded as a blueprint for conservatives on the key issue of the day. It would repeal the 2010 federal health care law, give states more say over Medicaid and limit government spending to 20 percent of the economy by 2015 – it’s been about 24 percent.

Under Ryan’s plan, there would be just two income-tax brackets, 10 percent for low-income earners and 25 percent for higher wage earners and corporations. The current top rate is 35 percent. Ryan said lost revenue would be made up for by closing loopholes in the tax code as well as through renewed economic growth, an assertion critics say is misguided.

Ryan’s Medicare plan would have no effect on current beneficiaries. People now under 55 would be able to choose traditional Medicare or private plans when they become eligible starting in 2023. If they selected a private program, the government would provide a payment to the insurer to help subsidize the cost. Seniors could pick plans from an exchange, and each insurer would have to offer a minimum level of benefits.

Ryan has said that such a system would force plans “to compete against each other to serve the patient (and) will help ensure guaranteed affordability.” Opponents say the change would wind up costing seniors more.

Ryan’s strengths are regarded as a command of budget details and a willingness to go out on limbs that ambitious politicians rarely are willing to take on. But his resume has one flaw: He’s shown few tendencies to engage in serious work with Democrats or moderates to fashion the kind of compromise that can pass Congress. Still, even skeptics laud him for his tenacity and willingness to tackle issues that other politicians have shied away from.

“I give him enormous credit for taking on this significant issue, something the president regrettably has failed to do," said Sen. Susan Collins, R-Maine, who opposed Ryan’s budget plans.